JP3734479B2 - Rare earth magnet manufacturing method - Google Patents

Description

【００４０】
表１に示したように、実施例によれば比較例よりも高い密着強度が得られ、塩水噴霧試験も合格であったのに対して、比較例では塩水噴霧試験において腐食がみられた。すなわち、磁石素体を溶解処理したのちに、ホウ酸塩緩衝溶液に浸漬処理するようにすれば、磁石素体と保護膜との密着性を向上させることができ、優れた耐食性を得られることが分かった。
【００４１】
以上、実施の形態および実施例を挙げて本発明を説明したが、本発明は、上記実施の形態および実施例に限定されるものではなく、種々変形することができる。例えば、上記実施の形態および実施例では、希土類磁石の製造工程について具体的に説明したが、全ての工程を含む必要はなく、また、他の工程を含んでいてもよい。
【００４２】
また、上記実施の形態および実施例では、磁石素体に第１の保護膜および必要に応じて第２の保護膜を設ける場合について説明したが、これら以外の他の構成要素を更に有していてもよい。例えば、磁石素体と第１の保護膜との間、第１の保護膜と第２の保護膜との間、あるいは第２の保護膜の上に、他の膜を有していてもよい。
【００４３】
【発明の効果】
以上説明したように、本発明による希土類磁石の製造方法によれば、磁石素体を酸により溶解処理したのち、ホウ酸およびホウ酸塩を含むホウ酸塩緩衝溶液に浸漬処理するようにしたので、磁石素体の酸化を抑制することができる。よって、磁石素体と保護膜との密着性を向上させることができ、耐食性を向上させることができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る希土類磁石の製造方法を表す流れ図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a rare earth magnet in which a protective film is provided on a magnet body containing a rare earth element.
[0002]
[Prior art]
As rare earth magnets, for example, Sm—Co ₅ series, Sm ₂ —Co ₁₇ series, Sm—Fe—N series, or R—Fe—B series (R represents a rare earth element) are known and have high performance. It is used as a permanent magnet. Among these, the R—Fe—B system mainly uses neodymium (Nd), which is more abundant than samarium (Sm) as a rare earth element and is relatively inexpensive, and iron (Fe) is also inexpensive. In particular, it has attracted attention because it has a magnetic performance equivalent to or better than that of the Sm—Co system.
[0003]
However, since this R—Fe—B rare earth magnet contains rare earth elements that are easily oxidized and iron as main components, the corrosion resistance is relatively low, and degradation and variations in performance are problems.
[0004]
In order to improve the low corrosion resistance of such rare earth magnets, it has been proposed to form various corrosion-resistant protective films on the surface (see Patent Documents 1 to 6).
[0005]
[Patent Document 1]
JP-A-60-54406 [Patent Document 2]
JP-A 63-198305 [Patent Document 3]
JP 63-217033 A [Patent Literature 4]
JP-A-1-286407 [Patent Document 5]
JP-A-2-26003 [Patent Document 6]
JP-A-9-7810 [0006]
[Problems to be solved by the invention]
However, although these protective films certainly improve the corrosion resistance of rare earth magnets, further improvements have been demanded. For example, when a protective film is formed by wet treatment such as plating or chemical conversion treatment, generally, as a pretreatment, an acid dissolution treatment and washing are performed, but in the washing step, the surface of the magnet body is oxidized. In some cases, the adhesion between the magnet body and the protective film may be reduced. As a result, if the protective film is damaged or there is a defect such as a pinhole in the protective film, the magnet body will corrode from there, thereby causing the protective film to swell or peel off, reducing the corrosion resistance. There was a problem that.
[0007]
The present invention has been made in view of such problems, and an object thereof is to provide a method for producing a rare earth magnet capable of improving corrosion resistance.
[0008]
[Means for Solving the Problems]
A method for producing a rare earth magnet according to the present invention is a method for producing a rare earth magnet in which a protective element is provided on a magnet body containing a rare earth element. After the magnet body is dissolved with an acid , boric acid and boric acid are produced. It includes a step of immersing in a borate buffer solution containing salt, and a step of forming a protective film on the magnet body after the immersion treatment.
[0009]
In the method for producing a rare earth magnet according to the present invention, since the magnet body is dissolved and then immersed in a borate buffer solution containing boric acid and borate , oxidation of the magnet body is suppressed. Therefore, the adhesion between the magnet body and the protective film is improved, and the corrosion resistance is improved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0011]
FIG. 1 shows a method for manufacturing a rare earth magnet according to an embodiment of the present invention. This method of manufacturing a rare earth magnet is to manufacture a rare earth magnet in which a protective film is provided on a magnet body containing a rare earth element. First, for example, a raw material powder of a magnet body is prepared (step S101). Specifically, for example, after casting an alloy having a desired composition containing a rare earth element and a transition metal element to produce an ingot, the obtained ingot is roughly pulverized to a particle size of about 10 μm to 800 μm by a stamp mill or the like. Further, it is pulverized into a powder having a particle size of about 0.5 μm to 5 μm by a ball mill or the like.
[0012]
The rare earth elements are yttrium (Y) and lanthanoid lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), which belong to group 3 of the long-period periodic table. 16 elements of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb) dysprosium (Dy) holmium (Ho) erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) It is a generic name.
[0013]
As the raw material powder, for example, a powder containing one or more rare earth elements, iron (Fe), and boron (B) is preferable. As the rare earth element, for example, at least one of neodymium, dysprosium, praseodymium, and terbium is preferably included.
[0014]
The rare earth element content is preferably 8 to 40 atomic%. If it is less than 8 atomic%, since the crystal structure becomes the same cubic structure as α-iron, a high coercive force (iHc) cannot be obtained, and if it exceeds 40 atomic%, there are many rare earth-rich nonmagnetic phases. This is because the residual magnetic flux density (Br) decreases.
[0015]
The iron content is preferably 42 atom% to 90 atom%. This is because if the iron content is less than 42 atomic%, the residual magnetic flux density decreases, and if it exceeds 90 atomic%, the coercive force decreases.
[0016]
The boron content is preferably 2 atomic% to 28 atomic%. If the boron content is less than 2 atomic%, the rhombohedral structure is formed, so that the coercive force is insufficient. If the boron content exceeds 28 atomic%, the boron-rich nonmagnetic phase increases and the residual magnetic flux density decreases.
[0017]
A part of iron may be replaced with cobalt (Co). This is because the temperature characteristics can be improved without impairing the magnetic characteristics. In this case, the substitution amount of cobalt is preferably in the range where x is 0.5 or less in terms of atomic ratio in terms of Fe _1-x Co _x . This is because if the substitution amount is larger than this, the magnetic characteristics are deteriorated.
[0018]
Further, a part of boron may be substituted with at least one of carbon (C), phosphorus (P), sulfur (S), and copper (Cu). This is because productivity can be improved and costs can be reduced. In this case, the content of carbon, phosphorus, sulfur and copper is preferably 4 atomic% or less. This is because if it exceeds the above range, the magnetic properties will deteriorate.
[0019]
Furthermore, the raw material powder includes aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), in order to improve coercivity, improve productivity, and reduce costs. Bismuth (Bi), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel (Ni), One or more of silicon (Si), gallium (Ga), copper (Cu), hafnium (Hf), etc. may be added. In this case, the total addition amount is preferably 10 atomic% or less of the total. This is because if it exceeds the above range, the magnetic characteristics will be deteriorated.
[0020]
In addition, the raw material powder may contain oxygen (O), nitrogen (N), carbon (C), calcium (Ca) or the like as an inevitable impurity within a range of 3 atomic% or less of the whole. .
[0021]
As the raw material powder for the magnet body, for example, a powder containing one or more rare earth elements and cobalt, or a powder containing one or more rare earth elements, iron, and nitrogen (N) is used. May be. Specifically, for example, those containing samarium and cobalt such as Sm—Co ₅ or Sm ₂ —Co ₁₇ (numbers are atomic ratios), or samarium and iron such as Sm—Fe—N The thing containing nitrogen is mentioned.
[0022]
In addition, when using 2 or more types of rare earth elements, you may make it use mixtures, such as a misch metal, as raw material powder.
[0023]
Next, this raw material powder is preferably molded in a magnetic field, and then sintered, for example, at 1000 ° C. to 1200 ° C. for 0.5 hour to 24 hours to produce a magnet body (step S102). At that time, the magnetic field strength is preferably 10 kOe or more, and the molding pressure is preferably about ¹ Mg / cm ² to ⁵ Mg / cm ² . The sintering atmosphere is preferably an inert gas atmosphere such as argon (Ar) gas or a vacuum. Subsequently, it is preferable to perform an aging treatment at 500 ° C. to 900 ° C. for 1 hour to 5 hours in an inert gas atmosphere. This aging treatment may be performed a plurality of times.
[0024]
Note that the magnet body may be produced by a method other than the sintering method. For example, you may make it manufacture by what is called a quenching method at the time of manufacturing a bulk magnet.
[0025]
After producing the magnet body, the magnet body is cut into a desired size and surface-polished by barrel polishing or the like (step S103). Next, the magnet body is degreased with an alkaline surfactant or the like (step S104). Subsequently, the magnet body is washed with water if necessary, and then dissolved with an acid such as a nitric acid solution to remove oxides on the surface of the magnet body (step S105).
[0026]
After the dissolution treatment, the magnet body is immersed in a borate buffer solution, and the deposits on the surface of the magnet body generated by the dissolution treatment are removed (step S106). At that time, ultrasonic waves may be applied. Thus, in this Embodiment, since the borate buffer solution is used, the oxidation of a magnet body is suppressed. The borate buffer solution means a buffer solution containing boric acid (H ₃ BO ₃ ) and a salt thereof. This borate buffer solution can be prepared by mixing boric acid and borax (sodium tetraborate decahydrate Na ₂ B ₄ O ₇ .10H ₂ O) in an appropriate amount to pH 6.5, pH 7.2. , PH 8.4, pH 10.4, etc., in the range of pH 6 to pH 11 can be prepared. Borate salts include ammonium pentaborate ((NH ₄ ) ₂ O · 5B ₂ O ₃ ), ammonium tetraborate ((NH ₄ ) ₂ B ₄ O ₇ ), potassium tetraborate (K ₂ B ₄ O ₇ ), lithium tetraborate (Li ₂ B ₄ O ₇ ), sodium peroxoborate (NaBO ₃ ), or a hydrate thereof may be used.
[0027]
In addition, after performing the dissolution process of step S105, before performing the immersion process of step S106, you may perform the water washing of the grade which removes an acid as needed. Moreover, you may wash with water as needed after performing the immersion process of step S106. However, it is preferable to perform the subsequent step of forming the first protective film (see step S107) without washing with water after the immersion treatment in step S106. This is because the oxidation of the magnet body can be suppressed.
[0028]
After that, a first protective film is formed on the magnet body by, for example, plating (step S107). The first protective film is preferably formed of, for example, nickel or an alloy containing nickel. Nickel is preferable because of its high productivity. From the viewpoint of hardness, durability, and corrosion resistance, nickel, cobalt, copper, zinc (Zn), phosphorus (P), boron, manganese (Mn) are used as necessary. An alloy of nickel containing at least one selected from the group consisting of tin (Sn) and tungsten (W) is preferred. The thickness of the first protective film is preferably 3 μm or more and 50 μm or less, for example, and more preferably 5 μm or more and 40 μm or less.
[0029]
After forming the first protective film, it is preferable to form a second protective film on the first protective film by plating, for example, if necessary (step S108). This is because the corrosion resistance can be further improved. The second protective film is preferably formed of an alloy containing nickel and sulfur, for example. From the viewpoint of productivity, an alloy of nickel and sulfur is preferable. From the viewpoint of hardness, durability, and corrosion resistance, iron, cobalt, copper, zinc, phosphorus, boron, manganese, tin, and tungsten are optionally used. An alloy containing at least one member selected from the group consisting of nickel and sulfur is preferable. The content of sulfur in the second protective film is preferably in the range of 0.01% by mass to 0.8% by mass. By including sulfur, the oxidation-reduction potential is lowered, and even if there is a pinhole, it becomes a sacrificial anode of the first protective film, and the overall corrosion resistance can be improved. For example, the thickness of the second protective film is preferably 1 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less.
[0030]
After forming the second protective film, post-processing is performed as necessary (step S109). Examples of the post-treatment include a phosphoric acid treatment for improving the adhesion with the yoke and a resin coating for insulation. After that, magnetization is performed (step S110). Thereby, a rare earth magnet is completed.
[0031]
Thus, according to the present embodiment, since the magnet body is dissolved and then immersed in the borate buffer solution, oxidation of the magnet body can be suppressed. Therefore, the adhesion between the magnet body and the first protective film can be improved, and the corrosion resistance can be improved.
[0032]
In particular, if a borate buffer solution having a pH of 6 to 11 is used, a higher effect can be obtained.
[0033]
【Example】
Furthermore, specific examples of the present invention will be described.
[0034]
A magnet body having a composition of 14Nd-1Dy-7B-78Fe (numbers are atomic ratios) is prepared by powder metallurgy, and heat-treated at 600 ° C. for 2 hours in an argon atmosphere (steps S101 and S102). (Refer to step S103) and processed into a size of 56 × 40 × 8 (mm) and further chamfered by barrel polishing.
[0035]
Next, the magnet body was washed with an alkaline surfactant (see step S104) and then dissolved with a nitric acid solution (see step S105). Subsequently, the magnet body was immersed in a boric acid-borax buffer solution of 25 ° C. and pH 8.4 mixed at a rate of 18.9 g / l boric acid and 0.72 g / l borax decahydrate and washed. (See step S106).
[0036]
After that, nickel was plated on the magnet body using a Watt bath to form a first protective film (see step S107). After forming the first protective film, post-processing was performed (see step S109), and magnetization was performed (see step S110). Thereby, the rare earth magnet of the example was obtained.
[0037]
As a comparative example for the example, a rare earth magnet was manufactured in the same manner as in the example except that the magnet body was immersed in deionized water at 25 ° C. and washed after the dissolution treatment.
[0038]
The obtained rare earth magnets of Examples and Comparative Examples were subjected to an adhesion strength test according to JIS-H-8630 and a salt spray test for 24 hours according to JIS-C-0023. In the salt spray test, the appearance was inspected with the naked eye, and pass / fail was judged by the presence or absence of rusting. The results are shown in Table 1.
[0039]
[Table 1]

[0040]
As shown in Table 1, according to the examples, adhesion strength higher than that of the comparative example was obtained, and the salt spray test was acceptable, whereas in the comparative example, corrosion was observed in the salt spray test. That is, if the magnet body is dissolved and then immersed in a borate buffer solution, the adhesion between the magnet body and the protective film can be improved, and excellent corrosion resistance can be obtained. I understood.
[0041]
The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the manufacturing process of the rare earth magnet has been specifically described. However, it is not necessary to include all the processes, and other processes may be included.
[0042]
Moreover, although the case where the first protective film and the second protective film as needed are provided on the magnet body has been described in the above-described embodiment and examples, the magnetic element body further includes other components. May be. For example, another film may be provided between the magnet body and the first protective film, between the first protective film and the second protective film, or on the second protective film. .
[0043]
【The invention's effect】
As described above, according to the method of manufacturing a rare earth magnet according to the present invention, the magnet body is dissolved in acid and then immersed in a borate buffer solution containing boric acid and borate . The oxidation of the magnet body can be suppressed. Therefore, the adhesion between the magnet body and the protective film can be improved, and the corrosion resistance can be improved.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method of manufacturing a rare earth magnet according to an embodiment of the present invention.

Claims (5)

A method for producing a rare earth magnet in which a protective film is provided on a magnet body containing a rare earth element,
A step of dissolving the magnet body with an acid and then immersing it in a borate buffer solution containing boric acid and borate ;
And a step of forming a protective film on the magnet body after performing the immersion treatment.   The method for producing a rare earth magnet according to claim 1, wherein the immersion treatment is performed in a borate buffer solution having a pH of 6 to 11.   The method for producing a rare earth magnet according to claim 1 or 2, wherein the protective film is formed by plating. The borate buffer solution is sodium tetraborate decahydrate as borate, or ammonium pentaborate, ammonium tetraborate, potassium tetraborate, lithium tetraborate, sodium peroxoborate or their hydration Including things
The method for producing a rare earth magnet according to any one of claims 1 to 3, wherein: The dissolution process removes oxides on the surface of the magnet body,
Remove the deposits on the surface of the magnet body generated by the melting process by the dipping process.
The method for producing a rare earth magnet according to any one of claims 1 to 4, wherein:

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